1. Technical Field
The present disclosure relates to a method for making an alignment mark on a substrate, such as a substrate that is subsequently used as a press mold.
2. Description of Related Art
With the ongoing development of optical imaging technology, wafer level lens modules are now widely used in electronic devices such as digital cameras, mobile phones, etc.
Generally, a wafer level lens module includes wafer level optical members, such as lenses, filters, etc, and a wafer level image sensor. In a process of manufacturing a wafer level lens module, a first wafer including many first wafer level optical members arranged in an array, a second wafer including many second wafer level optical members arranged in an array, and a third wafer including many wafer level image sensors arranged in an array are fabricated. Then in assembly, the first wafer is coupled to the second wafer, and subsequently is coupled to the third wafer to form a wafer level lens module array. Finally, the wafer level lens module array is cut into many individual wafer level lens modules by laser cutting. In the process of fabricating each of the first and second wafers, the first (second) wafer level optical members are formed by pressing a precision mold on a base material of the first (second) optical members arranged on a wafer. The precision mold includes a small substrate, which has many mold cavities arranged in an array therein.
When coupling the first wafer to the second wafer, the first wafer level optical members need to be precisely coaxial with the respective second wafer level optical members. Otherwise, so-called eccentricities occur. The eccentricities lower the quality of the wafer level lens modules. For assuring such coaxial alignment, at least one alignment mark is formed on the small substrate of the precision mold by a cutter. The alignment mark of the small substrate forms a corresponding alignment mark on each of the first and second wafers. Then when the first wafer is coupled to the second wafer, the alignment marks of the two wafers are aligned with each other. As a result, the first wafer level optical members can be coaxial with the respective second wafer level optical members.
However, because the edge of the cutter is rather thick, small alignment marks with narrower width cannot be formed on the small substrate of the precision mold.
Therefore, what is needed is a method for making an alignment mark on a substrate, which can overcome the limitations described above.